Write in front

CSDN topic challenge phase 1

• Event details address: CSDN

• Entry topic: front end interview collection

• Topic Description: welcome to join the topic creation partners. If I guess correctly, I think you should be a front-end person like me. Nowadays, the front-end accounts for an increasingly important proportion in the IT industry and has become an indispensable part. Front-end technologies are emerging one after another, and various technical categories and technical frameworks are also swarming out. The difficulty of front-end interview also increases. If we have a set of front-end interview dictionary. If you are a candidate: you can calmly solo interviewer, if you are an interviewer: you can torture the candidate to the bone!
  In short, we all gather our interview experience and learned knowledge here to form a set of front-end interview Dictionary of the system. Let readers have a great harvest whether in interview or study. Let's build a front-end interview dictionary hand in hand!!!

// Implementation of instanceof
function instanceofOper(left, right) {
  const prototype = right.prototype;
  while (left) {
    if ((left = left.__proto__) === prototype) {
      return true;
    }
  }
  return false;
}
// let obj  = {}
// Object.getPrototypeOf(obj) === obj.__proto__ ==> true

// Implement instanceof 2
function myInstanceof(left, right) {
  // Here, use typeof to judge the basic data type. If yes, return false directly
  if (typeof left !== "object" || left === null) return false;
  // getProtypeOf is the API of the Object object itself, which can get the prototype Object of the parameter
  let proto = Object.getPrototypeOf(left);
  while (true) {
    if (proto === null) return false;
    if (proto === right.prototype) return true; //Find the same prototype object and return true
    proto = Object.getPrototypeof(proto);
  }
}

Object.prototype.toString.call() returns [object Xxxx]

Deep copy and shallow copy

let obj = { b: "xxx" };
let arr = [{ a: "ss" }, obj, 333];

// assignment
let arr2 = arr;
// Shallow copy - only one layer is copied, and deep references still exist
// Object.assign(), ... Extension operator, slice, etc
let arr2 = arr.slice();
let arr2 = [...arr];
obj.b = "222"; // arr2[1].b => 222
// arr[2] = 4444 ==> arr2[2] ===> 333

// Deep copy
// 1. The simplest is JSON Stringify, but there is a problem with this. See the instructions below
let arr2 = JSON.parse(JSON.stringify(arr));

// 2. Self encapsulation and recursive processing

Realize deep copy - simple version

export function deepClone(obj, map = new Map()) {
  if (!obj && typeof obj !== "object") return obj;
  if (obj instanceof Date) return new Date(obj);
  if (obj instanceof RegExp) return new RegExp(obj.source, obj.flags);

  if (map.get(obj)) {
    //  If there is a circular reference, this object is returned
    return map.get(obj);
  }

  const cloneObj = obj.constructor(); // The of the array is [], and the object is {}

  map.set(obj, cloneObj); // Cache object for circular reference

  for (let key in obj) {
    if (obj.hasOwnProperty(key)) {
      cloneObj[key] = deepClone(obj[key], map);
    }
  }

  return cloneObj;
}

Write at the end

CSDN topic challenge phase 1

• Event details address: CSDN